German Patent No. 200 15 540 U1 discloses a switch element which is arranged on a rotary arm. This switch element swivels radially outwards in the event the film tears off or reaches its end and interacts with a signal generator arranged stationarily in the circular path of revolution of the rotary arm. The advantage is that this device does not require any power to be transmitted by the upper rotary arm bearing arrangement, inasmuch as the signal generator is arranged to be relatively stationary. However, it has the disadvantage if, due to functional unreliability that may occur in the event of varying film tensions. Moreover, a relatively large number of special parts are required.
The following applications disclose further embodiments: DT 2435785 A1, EP 0924133 A1 and WO 98/41450. In addition, film tear indicators for round baler/wrapper combinations of the type Rollant 250RC UNIWRAP, made by Claas and for example Type 65040 Kombi Goweil are commercially available. But the latter require relatively complex power transmission systems between rotary arm and frame.
The object of the invention is to improve apparatus of the types and to provide a simple and, in particular, less expensive solution.
This object is achieved according to the invention in that at least one optical sensor, ultrasonic sensor or sensor for electromagnetic radiations of different frequency ranges is associated with the wrapping material web portion between the wrapping material supply and the bale while the sensor is disposed stationarily.
This solution according to the invention operates independently of the tension of the wrapping material, so that not only through-tears in the wrapping material web but also holes caused by overstretching of the film or partial tears may be detected, which other known means are incapable of doing. Moving parts are not needed due to the stationary mounting of the sensors, whereby their adjustment is easily accomplished. Only relatively inexpensive standard elements are used, which may advantageously be integrated into an electronic control system of the machines.
In an advantageous embodiment, the optical sensor is in the form of a one-way light barrier with a receiver on the one side of the wrapping material web portion and with a transmitter arranged in alignment with the receiver on the other side of the wrapping material web portion. Infrared transmitters have proved useful due to their insensitivity to dust.
A structurally simple embodiment is provided by the use of a reflex sensor, which operates with reflected light or reflected sound waves and thereby detects whether a wrapping material web portion is present. Alternatively, X-rays or light sources of other light wavelengths may be used.
In a particularly dusty environment, provision is made for one or more sensors to be associated with a cleaning device.
Further features and advantages of the invention are revealed by the following description of an exemplary environment, with reference to a single Figure providing a schematic illustration thereof.